1. Field of the Invention.
This invention relates to catheterization of a patient and more particularly relates to a catheter from a blend of particular polyurethanes having a desirable balance of initial stiffness and softening when contacted by a body fluid.
2. Background of the Invention.
Catheterization procedures conventionally include puncture of a patient's skin and insertion of the catheter into a body cavity, such as the blood stream, using some sort of insertion device. For patient comfort and safety, it is highly desirable that the catheter be as soft as possible to aid in advancement through a tortuous blood vessel to a desired placement while minimizing the danger of puncture of the blood vessel wall. On the other hand, the material from which the catheter is fabricated must be stiff enough for skin puncture and advancement into a blood vessel without collapsing or kinking.
A number of polymeric materials have been investigated for fabrication of catheter tubing. Silicone rubber has been used, but this material, which is soft and pliable, requires inclusion of various additives such as fillers and plasticizers to give sufficient tensile strength and other desirable properties. The thick wall needed to prevent collapse due to the pliability requires a large outside diameter to achieve sufficient inside diameter for fluid flow. the portions of the polymer molecules which include the isocyanate and extender components and generally are of high crystallinity. The soft segments form from the polyether glycol portions of the polymer chains and generally are either noncrystalline or of low crystallinity. Crystallinity and hard segment content are factors which contribute to melt processability. Gould et al., in U.S. Pat. No. 4,454,309, discloses hydrophilic polyurethane diacrylate compositions which swell in water and may be molded and cured to form shaped products. A swellable catheter fabricated of a composition which includes a nonhydrophilic component and a hydrophilic polyurethane diacrylate component is marketed by Menlo Care Inc. under the tradename STREAMLINE.TM. and is disclosed in U.S. Pat. Nos. 4,781,703 and 4,994,047 to Walker et al. When contacted with a liquid, the composition swells and softens due to absorption of the liquid, causing the catheter to increase in cross-sectional area.
A softening and swelling catheter fabricated of a polyurethane synthesized from polyethyleneoxide soft segment is disclosed in U.S. Pat. No. 5,061,254 to Karakelle et al. of common assignee herewith.
A multilumen catheter marketed under the tradename FLEXTIP.TM. by Arrow International Corp., Wilmington, Del. and disclosed by Howes in U.S. Pat. No. Re. 31,873 and by Botterbusch et al. in U.S. Pat. No. 5,004,456 consists of a relatively soft distal end segment intended for insertion into a body cavity and a relatively hard rigid portion joined thereto by heat or pressure. The catheter segments are polyurethanes from aliphatic or aromatic diisocyanates.
Other catheters of the prior art have been made of rigid substantially inflexible polymeric materials. Exemplary of such conventional catheters are the catheters of fluorinated ethylene propylene copolymer (FEP) having stripes of FEP containing a radiopaque agent disclosed by Coneys in U.S. Pat. No. 4,657,024.
In recent years, polyurethanes have come to the fore as the preferred polymeric biomaterials for fabrication of various medical device components. Polyurethanes are synthesized from three basic components, a polyisocyanate, a polyglycol and an extender, usually a low molecular weight diol, diamine or water. If the extender is a diol, the polyurethane consists entirely of urethane linkages. If the extender is water or a diamine, both urethane and urea linkages are present.
The usual polyglycols are polyethylene qlycol (PEG) and polytetramethylene ether glycol (PTMEG). Polypropylene ether glycol (PPG), while providing a polyurethane of a desirable high softness, is infrequently used for polyurethanes intended for medical use because PPG requires a catalyst for reaction with isocyanates. The usual catalysts for polyurethane synthesis, such as octyl stanoate and dibutyl tin dilaurate, are toxic and contraindicated for medical grade polyurethane synthesis because of the danger of leachinq into a patient's body fluid.
Polyurethanes develop microdomains conventionally termed hard segments (HS) and soft segments, and as a result are often referred to as segmented polyurethanes. The hard segments form by localization of
A different approach to softening is disclosed in U.S. patent application Ser. No. 07/499,145 of common assignee herewith. A catheter of controlled softening is achieved by encapsulating a stripe of a hydrophobic stiffening polymer in a tubing of a hydrophilic thermoplastic base polymer.
While significant improvement in catheter performance has resulted from the above disclosures, there remains a need for a one piece catheter having the blood compatibility, softness and pliability of polyurethane which retains sufficient mechanical strength and stiffness for ease of insertion and repositioning if desired. The present invention addresses this need.